1. Field of the Invention
The invention relates to a method of honing bores, in particular, cylinder bores in crankcases of internal combustion engines.
2. Description of the Related Art
In truck engines, cylinder linings that are made by spin casting are often employed as piston bearing surfaces because this material is more wear resistant than the material of the engine block. Such cylinder liners however result in relatively high costs with regard to manufacture as well as assembly of the engine block. Therefore, it has already been proposed to partially harden the piston bearing surface of the engine block within the upper reversing area of the piston movement in order to achieve in this way a higher wear resistance. In this way, a separate cylinder liner is not needed. For example, hardening can be achieved by using a method employing a laser; however, the more economical and cost efficient alternative is induction hardening. When using induction hardening, non-concentric bore constrictions result; this prevents the use of conventional honing processes.
For processing partially hardened cylinder bores in crankcases, the method of coaxial honing has been developed; it is described, for example, in European patent 0 535 201 B1 or in VDI-Z, volume 6 (2001), pp. 49ff, in the article “Honen—Fortschritte durch optimierte Werkzeuge und Prozesse” (Translation: Honing—Advances through Optimized Tools and Processes) authored by U. Klink and G. Flores. The tool described in this article contains two sets of tool members that can be radially advanced or fed independently from one another. The lower set of tool members consists of hard metal guides that rest against the bore wall that has been pre-machined. In this way, the tool is oriented with regard to direction and central position relative to the bore axis. The diamond honing stones of the upper tool member set are subsequently expanded and machine the hardened bore section with the constrictions. The feed of both sets of tool members and thus their expansion is carried out separately. In this connection, feeding of guides can be realized hydraulically while the diamond honing stones are advanced electro-mechanically.